A night that was already bad in losing at home to Swansea got worse for Arsenal when goalkeeper Petr Cech was ruled out of Saturday's North London derby through injury.

In keeping with the calamitous nature of the evening in which Arsenal lost 2-1 having been 1-0 up to an understrength Swansea team, the goalkeeper was injured while returning to his goal having gone forward in a vain attempt to earn a late equaliser from a corner.

Despite the boos ringing out around the stadium at the final whistle, as well as those which greeted his decision to substitute goal-scorer Joel Campbell after an hour, manager Arsene Wenger insisted that his team had to remain positive.

"It was a very unlucky defeat because we created many chances, we were unlucky in our finishing and they only had two shots on target which were both goals," claimed Wenger. "It's a very disappointing result. The players are very down but we have to respond to that."

This league defeat was Arsenal's third consecutive defeat in all competitions after the losses to Barcelona and Manchester United but Wenger attempted to remain upbeat, despite revealing that defender Laurent Koscielny would also miss Saturday's derby game against Tottenham.

"We focus on our job and come back reminding ourselves that we have some quality as well. Of course we have to analyse it and bounce back," he said.

"At the moment I am worrying about our results. We just lost three games and that is always a very disappointing moment for the team. At the moment we don't dream. We have to be realistic and come back to what we do well, the basics."

One small positive from the night was that title rivals Spurs and Manchester City were also beaten, which underlined the unpredictable nature of the season.

"It is very difficult to say (who will win) because everybody drops points. We need to get back to positive results before we speak about the Championship which is at stake at the moment. It is very difficult as it is unpredictable," said Wenger.